4583812 1999-12-14 20:42 /428 rader/ Postmaster
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Ärende: CERT Advisory CA-99.15 - Buffer Overflows in SSH Daemon an
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RSAREF2 Library
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Date: Tue, 14 Dec 1999 10:20:48 -0800
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CERT Advisory CA-99-15 Buffer Overflows in SSH Daemon and RSAREF2
Library
Original release date: December 13, 1999
Last revised: --
Source: CERT/CC
A complete revision history is at the end of this file.
Systems Affected
* Systems running some versions of sshd
* Systems using products that use RSAREF2 (e.g., some SSL-enabled
web servers)
I. Description
Some versions of sshd are vulnerable to a buffer overflow that can
allow an intruder to influence certain variables internal to the
program. This vulnerability alone does not allow an intruder to
execute code.
However, a vulnerability in RSAREF2, which was discovered and
researched by Core SDI, can be used in conjunction with the
vulnerability in sshd to allow a remote intruder to execute
arbitrary code.
Additional information about the RSAREF2 vulnerability can be
found at
http://www.core-sdi.com/advisories/buffer%20overflow%20ing.htm
The RSAREF2 library was developed from a different code base than
other implementations of the RSA algorithm, including those from
RSA Security Inc. The vulnerability described in this advisory is
specific to the RSAREF2 library and does not imply any weakness in
other implementations of the RSA algorithm or the algorithm itself.
Also, only versions of SSH compiled with RSAREF support, via the
--with-rsaref option, are vulnerable to these issues.
The use of the RSAREF2 library in other products may present
additional vulnerabilities. RSAREF2 may be used in products such as
SSL-enabled web servers, ssh clients, or other cryptographically
enhanced products. Appendix A of this advisory will be updated with
new information as it becomes available regarding problems in other
products that use the RSAREF2 library.
II. Impact
Using the two vulnerabilities in conjunction allows an intruder to
execute arbitrary code with the privileges of the process running
sshd, typically root.
We are investigating whether vulnerabilities in other products may
expose the vulnerability in RSAREF2, and will update this advisory
as appropriate.
See Appendices A and B for more information that may affect the
impact of this vulnerability.
III. Solution
Apply patch(es) from your product vendor
Apply patch(es) to the RSAREF2 library. RSA Security Inc. holds a
patent on the RSA algorithm and a copyright on the RSAREF2
implementation. We encourage you to consult your legal counsel
regarding the legality of any fixes you are considering before
implementing those fixes. Please see RSA's vendor statement in
Appendix A.
Exploiting the vulnerability in RSAREF2 requires an application
program to call the RSAREF2 library with malicious input. For
products that allow an intruder to influence the data provided to
the RSAREF2 library, you may be able to protect against attacks by
validating the data they provide to RSAREF2.
Appendix A contains information provided by vendors for this
advisory. Appendix B contains information regarding test
performed by the CERT Coordination Center and other people, and
advice based on those tests. We will update the appendices as we
receive or develop more information. If you do not see your
vendor's name in Appendix A, the CERT/CC did not hear from that
vendor. Please contact your vendor directly.
Use a non-vulnerable implementation of the RSA algorithm
Sites not restricted by patent law may choose to use a
non-vulnerable implementation of RSA. Since RSA Security
Inc. holds a patent on the RSA algorithm, this option may not be
legally available to you. Please consult your legal counsel for
guidance on this issue.
Appendix A. Vendor Information
Compaq Computer Corporation
(c) Copyright 1998, 1999 Compaq Computer Corporation. All rights
reserved.
SOURCE:
Compaq Computer Corporation
Compaq Services
Software Security Response Team USA
Compaq's Tru64 UNIX is not vulnerable. Compaq does not ship ssl
Covalent Technologies
Covalent Raven SSL module for Apache
The Raven SSL module is not vulnerable to this attack since the SSL
library used does not use the RSAREF library.
Data Fellows Inc.
F-Secure SSH versions prior 1.3.7 are vulnerable but F-Secure SSH
2.x and above are not.
FreeBSD
FreeBSD 3.3R and prior releases contain packages with this
problem. This problem was corrected December 2, 1999 in the ports
tree. Packages built after this date with the rsaref updated
should be unaffected by this vulnerabilities. Some or all of the
following ports may be affected should be rebuilt:
p5-Penguin, p5-Penguin-Easy, jp-pgp, ja-w3m-ssl, ko-pgp, pgpsendmail,
pine4-ssl, premail, ParMetis, SSLtelnet, mpich, pipsecd, tund,
nntpcache, p5-Gateway, p5-News-Article, ru-pgp, bjorb, keynote,
OpenSSH, openssl, p5-PGP, p5-PGP-Sign, pgp, slush, ssh,
sslproxy, stunnel, apache+mod_ssl, apache+ssl, lynx-ssl,
w3m-ssl, zope
Please see the FreeBSD Handbook for information on how to obtain a
current copy of the ports tree and how to rebuild those ports which
depend on rsaref.
Hewlett-Packard Company
HP does not supply SSH. HP has not conducted compatibility testing
with version 1.2.27 of SSH, when compiled with the option
--with-rsaref. Further, RSAREF2 has not been tested to date. As far
as the investigation to date, HP appears to be not vulnerable.
IBM Corporation
IBM AIX does not currently ship the secure shell (ssh) nor do the
base components of AIX ship or link with the RSAREF2 library.
IBM and AIX are registered trademarks of International Business
Machines Corporation.
Microsoft
The Microsoft Security Response Team has investigated this issue,
and no Microsoft products are affected by the vulnerability.
NetBSD
NetBSD does not ship with ssh in either its US-only or
International variants at this time, so no default installation of
NetBSD is vulnerable.
However, ssh is installed and widely used by many NetBSD
installations, and is available from our software package tree in
source form. The NetBSD ssh package can be compiled either with or
without RSAREF2, settable by the administrator at compile time
according to local copyright and license restrictions.
Installations which used RSAREF2 in compiling ssh are vulnerable,
and we recommend recompiling without RSAREF2 if their local legal
situation permits.
In addition, the following list of software packages in the NetBSD
"packages" system are also dependent on the RSAREF2 library:
* archivers/hpack
* security/openssl
* security/pgp2
* security/pgp5
* www/ap-ssl
of those, the security/openssl package is itself a library, and the
following packages depend on it:
* net/ppp-mppe
* net/speakfreely-crypto
* www/ap-ssl
We recommend recompiling and reinstalling these packages without
RSAREF2, if your local legal situation permits.
Network Associates, Inc.
After a technical review of the buffer overflow bug in RSAREF, we
have determined at Network Associates that PGP is not affected by
this bug, because of the careful way that PGP uses RSAREF.
This applies to all versions of PGP ever released by MIT, which
are the only versions of PGP that use RSAREF. All other versions
of PGP, such as the commercial versions and the international
versions, avoid the use of RSAREF entirely.
Philip Zimmermann
10 December 1999
[CERT/CC Note: A PGP signed copy of this information and additional
technical details are available as well.]
OpenSSL
OpenSSL with RSAREF is not vulnerable.
OpenBSD / OpenSSH
More information is available from:
http://www.openbsd.org/errata.html#sslUSA
RSA Security Inc.
RSA Security Inc. recommends that developers implement the
proposed or similar patch to RSAREF version 2.0 or otherwise to
ensure that the length in bits of the modulus supplied to RSAREF
is less than or equal to MAX_RSA_MODULUS_BITS.
RSA Security Inc. is no longer distributing the RSAREF toolkit,
which it offered through RSA Laboratories in the mid-1990s as a
free, source implementation of modern cryptographic
algorithms. Under the terms of the RSAREF license, changes to the
RSAREF code other than porting or performance improvement require
written consent. RSA Security hereby gives its consent to
implement a patch to RSAREF to address this advisory.
This advisory only applies to RSAREF, not RSA Security's current
toolkits and products, which were developed independently of
RSAREF.
Although RSA Security is no longer distributing RSAREF, the
toolkit is still available in a number of "freeware" products such
as SSH under RSA Security's original RSAREF v2.0 software license
("license.txt", March 25, 1994), which is distributed along with
those products. As a reminder, that license limits the use of
RSAREF to noncommercial purposes. RSAREF, RSAREF applications, and
services based on RSAREF applications may not be sold, licensed or
otherwise transferred for value. (There is a minor exception for
small "shareware" deployments as noted in the "info.txt" file,
March 25, 1994.)
SSH Communications
The bug only affects ssh when it is compiled with RSAREF (i.e.,
only when --with-rsaref is explicitly supplied on the command
line). Any version compiled without --with-rsaref is not
affected. The problem should not affect users of the commercial
versions (who are licensed to use the built-in RSA) or users
outside the United States (who are presumably not using RSAREF and
can use the built-in RSA without needing a license). I.e., only
those non-commercial users who actually compile with a separately
obtained RSAREF should be affected.
The bug is present in all versions of SSH1, up to and including
1.2.27. It will be fixed in ssh-1-2.28 (expected to go out in a
few days to fix this problem). It does not affect SSH2. (Please
note that ssh1 is no longer maintained, except for security fixes,
due to certain rather fundamental problems that have been fixed in
ssh2.)
Any implementation compiled without an explicitly specified
--with-rsaref is not affected by this problem.
A patch provided by SSH Communications is available from the
CERT/CC web site. This version of the patch has been signed by the
CERT/CC.
Stronghold
Stronghold does not use RSAREF and is unaffected.
Appendix B. CERT/CC and Other Third-Party Tests
RSAREF Patch from Core SDI and the CERT/CC
With the assistance of Core SDI, the CERT Coordination Center
tested sshd version 1.2.27 running on an Intel-based RedHat Linux
system and found that configuration to be vulnerable. Tests
conducted by Core SDI indicate that sshd 1.2.27 running on OpenBSD
and FreeBSD on Intel is also vulnerable, and it is likely that
other configurations are vulnerable as well.
CERT/CC has developed a patch for the RSAREF2 vulnerability based
in part on work done by Core SDI. This patch is available at
ftp://ftp.core-sdi.com/pub/patches/rsaref2.patch
http://www.cert.org/advisories/CA-99-15/rsa-patch.txt
You can verify this patch with a detached PGP signature from the
CERT/CC.
We believe the patch originally provided by Core SDI in their
advisory may not be a complete fix to this particular problem. We
have worked with them to develop an updated patch and gratefully
acknowledge their contribution to the fix provided here. Neither
the CERT/CC, the Software Engineering Institute, nor Carnegie
Mellon University provides any warranties regarding this
patch. Please see our disclaimer at the end of this advisory.
Possible vulnerability of ssh clients
The possible vulnerability of ssh clients is of particular
concern. As we learn more regarding the vulnerability of ssh
clients, we will update this advisory. One possible way to attack
an ssh client would be to construct a malicious ssh server and
lure or trick victims into connecting to the server. The ssh
client will warn users when it connects to a site that presents a
key that does not match one previously associated with the
server. The dialog may be similar to
the following:
% ssh badhost
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the host key has just been changed.
Please contact your system administrator.
Add correct host key in /etc/.ssh/known_hosts to get rid of this message.
Are you sure you want to continue connecting (yes/no)? no
%
If you see this warning, you should answer "no" to the prompt and
investigate why the key you received does not match the key you
expected.
_________________________________________________________________
The CERT Coordination Center would like to thank Alberto Solino
<Alberto_Solino@core-sdi.com> and Gerardo Richarte
<Gerardo_Richarte@core-sdi.com> of Core SDI S.A. Seguridad de la
informacion, Buenos Aires, Argentina (http://www.core-sdi.com), who
discovered the problem in RSAREF2 and provided valuable technical
assistance. We would also like to thank Andrew Cormack of JANET CERT,
who provided technical assistance; Theo de Raadt of the OpenBSD
project, who provided valuable feedback used in the construction of
this advisory; Burt Kaliski of RSA Security Inc.; and Tatu Ylonen of
SSH Communications Security.
______________________________________________________________________
This document is available from:
http://www.cert.org/advisories/CA-99-15-RSAREF2.html
______________________________________________________________________
CERT/CC Contact Information
Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.
CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) /
EDT(GMT-4) Monday through Friday; they are on call for emergencies
during other hours, on U.S. holidays, and on weekends.
Using encryption
We strongly urge you to encrypt sensitive information sent by
email. Our public PGP key is available from
http://www.cert.org/CERT_PGP.key
If you prefer to use DES, please call the CERT hotline for more
information.
Getting security information
CERT publications and other security information are available from
our web site
http://www.cert.org/
To be added to our mailing list for advisories and bulletins, send
email to cert-advisory-request@cert.org and include SUBSCRIBE
your-email-address in the subject of your message.
Copyright 1999 Carnegie Mellon University.
Conditions for use, disclaimers, and sponsorship information can be
found in
http://www.cert.org/legal_stuff.html
* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.
______________________________________________________________________
NO WARRANTY
Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
fitness for a particular purpose or merchantability, exclusivity or
results obtained from use of the material. Carnegie Mellon University
does not make any warranty of any kind with respect to freedom from
patent, trademark, or copyright infringement.
_________________________________________________________________
Revision History
December 13, 1999: Initial release
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